Structure-Tectonics

David Brumbaugh: Geophysics & structural geology

Research activities

Mechanics
of normal and thrust faulting; earthquake source mechanics; Cenozoic tectonics
of the southern Colorado Plateau and transition zone; earthquake studies of the
North Anatolian fault zone, Turkey, and the Aleutian plate boundary.

Ernie Duebendorfer: Structural geology & tectonics

Research activities

My research
interests lie in the fields of structural geology and tectonics and are quite
broad. All of my research projects are strongly field based and many are
augmented with petrographic, microstructural, and microprobe work. In addition,
I work regularly with U/Pb and 40Ar/39Ar geochronologists to constrain the
timing of deformational events. I currently have two active research projects.

Proterozoic
accretionary tectonics in the southwestern U.S. The period between 1780 and
1650 Ma was one of major crustal growth in North America. Crustal growth
occurred by the generation, collision, and amalgamation of juvenile crustal
material such as oceanic island arcs and their associated basins, magmatic
additions to the crust through rifting and, possibly, the involvement of
fragments of older continental crust. This accretionary episode was similar in
scale to the addition of numerous “suspect” terranes to western North America
in the Mesozoic. A complicated and enigmatic boundary zone between the Mojave
and Yavapai Proterozoic crustal provinces occurs in northwestern Arizona.
Determining the timing and mode of juxtaposition those provinces and the manner
in which isotopically mixed crust is formed are the primary objectives of this
work.

Tertiary
extensional tectonics in southern Nevada and northwestern Arizona. The Lake
Mead area, southern Nevada and northwestern Arizona, has been the locus of
large-magnitude extension (perhaps as much as 300%, according to some workers)
in the middle Miocene and studies in this region have been the basis for
development of several models for crustal extension. A major question has
centered on the types of structures that have accommodated extension,
specifically, the relative roles of strike-slip and detachment faulting. An
outgrowth of this project focuses on how along-strike variations in
displacement along large-scale, low-angle normal fault systems (detachments)
are accommodated.

Harlan,
S.S., Duebendorfer, E.M., and Deibert, J., 1998, 40Ar/39Ar age determinations
from Miocene volcanic rocks in the western Lake Mead area and in the southern
Las Vegas Range: Canadian Journal of Earth Sciences, v. 35, p. 495-503.

Paul Umhoefer: tectonics, basin analysis & structure

Research activities

My research is focused on Tectonics, especially active and
young tectonics of Late Cenozoic time. My main research interest is in the
tectonic evolution of, and processes that form, oblique plate boundaries. More
specifically, I study basins and related faults that form in these settings,
and the processes and evolution of areas with mixed strike-slip and dip-slip
faulting. My research is field based and my students and I use the methods of
structural geology, stratigraphy, and related disciplines to understand tectonic
problems. The research I conduct is inevitably collaborative with researchers
in many other fields, but especially in paleontology, sedimentology,
geochronology, petrology, marine seismology, geodesy, and paleomagnetism.